Conventionally as a manufacturing method of the multilayer printed circuit board that has conductive patterns formed on both sides, there is a method of laminating a plurality of resin films where the conductive patterns are formed only on one side thereof (refer to Japanese Patent Application Laid-Open Publication No. 2003-86948, for example).
In this manufacturing method, first, a plurality of resin films each of which has the same thickness are prepared.
Next, among the plurality of resin films, two arbitrary resin films are laminated so that the sides where the conductive patterns are not formed face each other.
Then, other remaining resin films are laminated so that the sides where the conductive patterns are formed and the sides where the conductive patterns are not formed face each other.
Then, the multilayer circuit board is manufactured by pressure heating the laminated resin films.
According to this manufacturing method, since only the resin film where the conductive patterns are formed on one side is used, a process of forming the conductive patterns on both sides of the resin film becomes unnecessary so that the manufacturing process of the multilayer printed circuit board can be simplified as compared with a case where both resin films where the conductive patterns are formed on one side and resin films where the conductive patterns are formed on both sides are used together.
Moreover, when using resin films each having different thickness, the resin films having each thickness must be manufactured separately. However, according to the manufacturing method mentioned above, since only the resin films each having a single thickness are manufactured, the manufacturing process of the multilayer printed circuit board can be simplified.
However, since the resin films each having the same thickness are laminated, the following problem arises in the multilayer printed circuit board after manufacturing in the above-mentioned conventional manufacturing method.
That is, when considering a thickness of dielectrics disposed between the conductive patterns of the adjoining resin films, a resin thickness of a single resin film equals the thickness of the dielectric in a portion where the other resin films are laminated.
On the other hand, a resin thickness of two resin films equals to the thickness of the dielectric in a portion where the two resin films are laminated.
Thus, since the thicknesses of the dielectrics differ in the portion where the above-mentioned two resin films are laminated and the portion where the other resin films are laminated, a formula for obtaining an impedance of the transmission line of the high-frequency signal may become complicated when forming the high frequency circuit in the multilayer printed circuit board.
For example, when the conductive patterns of the portion where the above-mentioned two resin films are laminated are used as the transmission line, as compared with a case where the conductive pattern of the portion where the other resin films are laminated is used, intervals between the transmission line and the conductive pattern positioned outside of the transmission line will differ.
For this reason, influences that the dielectric thicknesses between the transmission line and the conductive pattern in outer side of the transmission line have on the impedance differ.
Therefore, if the conductive patterns of the portion where the above-mentioned two resin films are laminated are used as the transmission line, the formula for calculating the impedance of the transmission line becomes complicated, and circuit design will be very complicated.
Moreover, when the conductive patterns on both sides of the multilayer printed circuit board are assigned to ground lines, and the conductive patterns inside the multilayer printed circuit board are used as the transmission lines of the high-frequency signal, intervals between the transmission lines and the ground lines will differ in one side and another side in a laminating direction when the number of the resin films that constitute the multilayer printed circuit board is an odd number.
That is, the transmission line becomes offset from a center of the laminating direction of the multilayer printed circuit board.
For this reason, the formula for calculating the impedance of the transmission line becomes complicated, and circuit design will be very complicated.